Groovy, didn't know that. When I said "not mature" I just meant in terms of number of deployments and age of the code-base.
No knock against author intended.
You might underestimate the size of deployments of logstash. Mailchimp runs logstash in a pretty sizeable cluster for all traffic coming into HTTP front-ends. I can think of quite a few sizeable logstash installs that I can't mention.
whack (author of logstash) works at dreamhost now, and is indeed working on logstash full-time.
The kibana ui is, afaik, being ported to ruby atm.